Add a test for correct default field values.

* examples/example_smallbusiness.glom: Add a string default
  value, so we can test it. There are already some numeric
  default values.
* Makefile_tests.am:
* tests/test_selfhosting_new_from_example_defaultvalues.cc:
  Check some default values.
Fix a typo in the header blocks.

Some file had this typo and was probably then copied into new files.